Dual stage axially injected reentrant stream crossed-field tube



A ril 21, 1970 G. K. FARNEY 3 5 DUAL STAGE AXIALLY INJECTED REENTRANT STREAM CROSSED-FIELD TUBE Filed 001;. 5. 1967 l6 INVENTOR.

BY $55 K. ARNEY RNEY United States Patent US. Cl. SIS-39.3 10 Claims ABSTRACT OF THE DISCLOSURE A dual stage axially injected reentrant stream crossedfield tube is disclosed. The tube includes a cylindrical nonernissive cathode sole surrounded by axially spaced first and second slow wave circuits to define a pair of axially spaced circular crossed-field interaction regions or stages. An electron gun is provided at one end of the crossedfield interaction regions for projecting an annular beam of electrons axially through the interaction regions to a collector structure disposed at the opposite end of the interaction regions. Signal wave energy to be amplified is applied to the slow wave circuit in the first stage. The signal energy cumulatively interacts with the electron stream to produce rotating spokes of space charge in the axially drifting stream. The spokes of space charge drift axially into the second crossed-field interaction region for exciting microwave energy on the second slow wave circuit. Cumulative interaction with the second slow wave circuit in the second stage produces an amplified output signal which is extracted and fed to a suitable load. In a preferred embodiment, the second slow Wave circuit is operated at a DC. potential substantially higher than the DC potential applied to the anode slow wave circuit in the first stage for improving the efiiciency and gain of the tube. For example, in the first crossed-field interaction region the slow wave circuit is operated with a voltage V which is typically 4 to times the synchronous voltage V However, in the second stage the slow wave circuit is operated at a potential which is between and 25 times the synchronous voltage V Description of the prior art directed group velocity and do not substantially interact with the circumferentially directed wave energy on the radio frequency circuit. Therefore, noise signals are not substantially coupled to the wave circuit and, therefore, the tube is capable of amplification down into the low signal regime, there-by greatly extending the dynamic range of the amplifier tube.

Although such a tube has substantially improved dynamic range it is desired to improve the efiiciency and gain of the tube.

Summary of the present invention The principal object of the present invention is the provision of an improved axially injected reentrant stream crossed-field amplifier tube.

One feature of the present invention is the provision, in an axially injected reentrant stream crossed-field amplifier tube, of a second slow wave circuit axially spaced 3,508,110 Patented Apr. 21, 1970 along the crossed-field interaction region from a first slow wave circuit such that rotating spokes of space charge produced by interaction in the first state drift axially into a second interaction region or stage for cumulative interaction with wave energy on the second slow wave circuit to produce output R.F. energy.

Another feature of the present invention is the same as the preceding feature wherein the anode voltage applied to the second slow wave circuit is substantially greater than the anode voltage applied to the first slow wave circuit, whereby the efiiciency and gain of the tube is substantially improved.

Another feature of the present invention is the same as any one or more of the preceding features wherein the first and second slow wave circuits are resistively terminated at the output end of the first slow wave circuit and the input end of the second slow wave circuit to prevent undesired oscillations.

Another feature of the present invention is the same as any one or more of the preceding features wherein the first and second slow :wave circuits include circuit severs and the severed portion of the second slow wave circuit is angularly rotated relative to the position of the circuit sever of the first slow wave circuit such that the rotating spokes of space, which drift into the stage, are well formed at the entrance to the second slow wave circuit.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanyin drawings wherein:

Brief description of the drawings FIG. 1 is a fragmentary perspective view of a dual stage axially injected reentrant stream crossed-field amplifier incorporating features of the present invention,

FIG. 2 is an enlarged sectional view of a portion of FIG. 1 taken along line 2-2 in the direction of the arrows, and

FIG. 3 is a schematic transverse sectional line diagram depicting relative angular displacement of the first and second slow wave circuits.

Description of the preferred embodiments Referring now to the drawings, there is shown a dual stage axially injected reentrant stream crossed-filed amplifier tube 1 incorporating features of the present invention. The tube 1 includes a centrally disposed cylindrical non-emissive cathode electrode or sole 2 surrounded by first and second annular slow wave circuits 3 and 4, respectively. The slow Wave circuits 3 and 4 are axially spaced along the non-emissive sole 2 and are radially spaced from the sole to define first and second crossedfield interaction regions or stages 5 and 6, respectively. Suitable slow wave circuits 3 and 4 including toroidal shaped helices including a solid block of conductive metal forming circuit severs 7 and 8 for each of the slow Wave circuits.

An electron gun assembly 9 is disposed at one axial end of .the combined crossed-field interaction regions 5 and 6 for projecting an annular stream of electrons axially through the interaction regions 5 and 6. The electron gun 9 includes a cylindrical thermionic cathode emitter 11 having a suitable heating element 12 for heating same to thermionic emission temperature. An annular accelerating electrode 13 surrounds the cathode emitter 11 for pulling the electrons from the emitter 11. A repeller electrode 14, operating at cathode potential, is disposed at one end of the cathode emitter 11 to cooperate with the anode potential applied to the accelerating electrode 13 for causing the electrons emitted from the emitter 11 to be projected in the axial direction into and through the interaction regions 5 and 6. A magnet structure, not shown, produces an axially directed magnetic field B through the magnetron interaction regions 5 and 6 and through the annular space between the cathode emitter 11 and the accelerating electrode 13. Although the electron gun 9 has been described as a magnetron injection gun, it can also take the form of an annular electron emitter of the type employed for type tubes combined with an annular accelerating electrode disposed between the emitter and the first interaction region for producing the annular electron beam.

A beam collector electrode structure 15 is disposed at the other axial end of the interaction regions 5 and 6 for collecting the electron beam after passage through the interaction regions 5 and 6. The beam collector structure 15 includes a plurality of cup-shaped collector electrodes 16 of progressively larger diameter taken in the axial direction of the tube with insulator members 17 positioned between adjacent collector electrodes 16 such that the electrodes may be operated at independent potentials. A vacuum tight envelope structure 18, as of copper, encloses the various tube parts and is evacuated to a suitably low pressure as of torr. Thermally conductive electrical insulator members 19, as of ceramic, are joined to the envelope 18 and to the slow wave circuits 3 and 4 for supporting and insulating the slow wave circuits 3 and 4 with respect to each other to permit independent D.C. potentials to be applied thereto.

A DC. power supply 21, schematically indicated by battery 22 and potential dividing network 23, supplies independent operating potentials to various ones of the electrode structures within the tube 1. More specifically, pick-off 24 supplies a certain negative potential relative to ground to the cathode emitter 11 via lead 25 and the same potential is applied to one of the beam collector electrodes 16 via lead 25. Pick-off 26 supplies a potential to the non-emissive sole 2 'which is slightly negative with respect to the potential applied to the cathode emitter 11. Pick-off 27 supplies a potential positive with respect to the emitter 11 to the accelerating electrode 13 via lead 28 and the same potential is applied via lead 28 to a second one of the beam collector electrode structures 16". The first slow wave circuit 3 is operated at ground potential which is slightly positive with respect to the potential applied to the accelerating electrode 13. Pickoff 29 supplies a relatively high positive potential to the second slow wave circuit 4 via lead 31, feedthrough insulator 32 and R.F. choke 33. Pick-off 34 supplies a potential intermediate the potential applied to the second slow wave circuit 4 and ground potential via lead 35 to a fourth one of the beam collector electrodes 16". The innermost beam collector electrode 16 is operated at the same potential as the sole 2.

An R.F. input line 36, such as coaxial line, is connected .to the input end of the first slow wave circuit 3 for applying microwave R.F. signals to be amplified to the slow wave circuit 3. The output end of the first slow wave circuit 3 is connected via a coaxial line 37 to a matched resistive termination 38. The input end of the second slow wave circuit 4 is connected via a coaxial line 39 to a matched resistive termination 41. The output end of the second slow wave circuit 4 is connected via a coaxial line 42 to an output load, not shown. A filament supply voltage as of 6 volts is applied across the filamentary heater 12 from a battery 43.

In operation, input R.F. signals to be amplified are applied to the first slow wave circuit 3 via input coaxial line 36. The R.F. wave traveling in the circumferential direction on the first slow wave circuit 3 produces cumulative electronic cross-field type interaction with the electrons in the first interaction region 5 to produce spokes of space charge e which rotate about the cathode sole 2 in the magnetron interaction region 5. The spokes of space charge e cumulatively interact with the R.F. wave on the first slow wave structure producing amplification of the wave and more clearly defined spokes of space charge. The amplified R.F. wave is extracted via coaxial line 37 and terminated in impedance matching resistive load 38.

The circuit sever 7 debunches those spokes of space charge which traverse the sever 7 in the circumferential direction to prevent electronic feedback and oscillation in the first stage of the tube. However, due to the axial drift of the electron stream, certain of the well defined spokes of space charge drifting through from the last half of the first slow wave circuit 3 to the second stage 6 do not pass the sever 7. These spokes drift into the second stage 6 to excite Wave energy on the second slow wave circuit 4. The circuit sever portion 8 of the second slow wave circuit 4 is preferably angularly displaced with respect to the circuit sever 7 of the first slow wave circuit 3 such that the well formed spokes of space charge which areproduced near the output end of the first slow wave circuit 3 drift into the input end of the second slow wave circuit 4. Such a condition is obtained when the circuit sever 8 is in an angular position as indicated in FIG. 3. Namely, the circuit sever is rotated in the upstream direction from the circuit sever 7 of the first section. The R.F. wave excited on the second slow wave circuit 4 cumulatively interacts with the electron stream producing an amplified output at output terminal 42.

In the absence of an input signal to be amplified, the electrons of the beam remain in a relatively small diameter annulus closely following the original dimensions of the beam annulus injected into the magnetron interaction regions 5 and 6. These electrons drift through the magnetron interaction region and are collected on the collector electrode structure 16. Noise signals in the electron stream have substantially no circumferential component and, therefore, do not substantially coup-1e to the slow wave circuits 3 and 4 to produce noise output. The tube, in the quiescent state, can be relatively efficient since the electron stream can be collected at substantially the same potential as the electrons have upon entering the first interaction region 5, that is, most of the electronswill be collected on the innermost collector electrodes 16 and 16', providing a type of depressed collector operation.

However, in the presence of a strong R.F. signal on the first slow wave circuit 3, the R.F. fields interact with the electrons to produce the rotating spokes and, in addition, the interacting electrons move further out from the cathode sole 2 toward the first anode slow wave circuit 3. A relatively small percentage of the electrons are collected on the first slow wave circuit 3 and a preponderance of the electrons flow into the second crossed-field interaction region 6. In the second interaction region 6, the anode potential is substantially greater than that applied in the first stage 5, for example, 10 to 25 times the synchronous voltage as compared to only 4 to 5 times the synchronous voltage for the anode potential applied to the first slow wave circuit. Accordingly, the efiiciency and gain in the second interaction region 6 is substantially greater than that produced in the first interaction region 5. In the second interaction region 6, the anode slow wave circuit 4 is spaced a greader radial distance from the cathode sole 2 than in the first interaction region 5 in order to maintain the same phase velocity in the two sections with the higher anode voltage applied in the second interaction region 6. In addition, the slow wave circuit 4, in the second interthat of the slow wave circuit 3 in the first interaction reaction region 6, preferably has a greater axial extent than gion 5 in order to obtain greater interaction with the beam.

Since many changes could be made in the above constructi'on and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a crossed-field tube apparatus; means forming concentrically spaced anode and substantially non electron emissive cathode sole stuctures for defining an annular crossed-field interaction region in the space therebetween; means for directing a magnetic field axially through said interaction region; means forming an electron gun structure disposed at one axial end of said interaction region for projecting a beam stream of electrons axially through said interaction region; means disposed at the other axial end of said interaction region for collecting the electron beam stream after passage thereof through said interaction region; said anode structure means including, a first slow wave circuit portion formed and arranged adjacent said interaction region for radio frequency power fiow thereon in a direction circumferentially directed of said interaction region, the improvement wherein, said anode structure means includes, a second slow wave circuit portion axially spaced along said interaction region from said first slow wave circuit portion, said second slow wave circuit portion being formed and arranged adjacent said interaction region for radio frequency power flow thereon in a direction circumterentially directed of said interaction region, and means for extracting radio frequency power from said second slow wave circuit portion.

2. The apparatus of claim 1 including, means for applying separate D.C. operating potentials to said first and second slow wave circuit portions of said anode structure.

3. The apparatus of claim 1 including means for applying radio frequency signals to be amplified to said first slow wave circuit portion.

4. The apparatus of claim 1 wherein said crossed-field interaction region has a radial thickness which is larger in the region adjacent said second slow wave circuit portion than in the region adjacent said first slow wave circuit portion.

5. The apparatus of claim 1 wherein the axial length of said second slow wave circuit portion is greater than the axial length of said first slow wave circuit portion.

6. The apparatus of claim 1 wherein said first and second slow wave circuit portions each include a circuit sever portion and wherein said sever portion of said second slow wave circuit is rotationally displaced relative to the position of said first circuit sever portion of said first slow wave circuit.

7. The method for producing a radio frequency output comprising the steps of axially injecting a beam stream of electrons through a first annular crossed-field interaction region defined between concentrically spaced anode and non electron emissive cathode structures with the interaction region containing an axially directed unidirectiontional magnetic field and a radially directed unidirectional electric field, cumulatively interacting the electrons of the beam stream with radio frequency wave energy flowing circumferentially of the axially directed beam stream on a first slow wave circuit to form in the first interaction region spokes of space charge which rotate about the axis in the beam stream, axially passing the beam stream with the rotating spokes of space charge through a second annular crossed-field interaction region defined between concentrically spaced anode and non electron emissive cathode structures and axially spaced from the first interaction region, the second crossed-field interaction region containing an axially directed unidirectional magnetic field in and a radially directed unidirectional electric field, causing the rotating spokes of space charge to excite a radio frequency wave on a second slow Wave circuit, and cumulatively interacting the rotating spokes of space charge with the radio frequency wave energy flowing circumferentially of the axially directed beam stream on the second slow wave circuit to produce output radio frequency wave energy on the second slow wave circuit.

8. The method of claim 7 including the steps of applying radio frequency wave energy to one end of the first slow Wave circuit to produce the rotating spokes of space charge in the first crossed-field interaction region.

9. The method of claim 7 including the steps of resistively terminating the output end of the first slow wave circuit and the input end of the second slow wave circuit.

10. The method of claim 7 including the steps of applying an electrical potential difference between the first and second concentric anode and cathode structures defining the first and second crossed-field interaction regions to produce the radially directed electric fields, and applying a larger potential difference to the second crossed-field interaction region than to the first interaction region.

References Cited UNITED STATES PATENTS 2,760,111 8/1956 Kumpfner 31539.3 2,859,380 11/1958 Dench 3153.6 X 2,976,455 3/1961 Birdsall et al. 3153.6 3,123,735 3/1964 Hull 3153.6 3,253,230 5/1966 Osepchuk 3153.6

ELI LIEBERMAN, Primary Examiner S. CHATMON, JR., Assistant Examiner US Cl. X.R. 

